The present invention relates to a method for detecting the concentration of the hydrogen peroxide vapor in a treatment vessel and an apparatus for practicing the method where hydrogen peroxide vapor is supplied to a treatment vessel to conduct a treatment, such as a sterilization treatment, by means of contact of the subject to be treated in the treatment vessel with hydrogen peroxide vapor.
Since hydrogen peroxide vapor is naturally decomposed into harmless oxygen and water by contact with a solid and generates nascent oxygen having a sterilizing effect and the like, it is a safe and simple agent for various treatments such as a sterilization and the like, and a wide range of utilization thereof is expected. In the field of manufacturing of medicines and medical instruments, and in the field of foods processing, packaging materials for the ground materials of medicines and foods have been heretofore subjected to the sterilization treatment by the hydrogen peroxide vapor. That is, the sterilization treatment of the subject to be treated is performed by contact with the hydrogen peroxide vapor, which is supplied into a treatment vessel which has housed therein the subject to be treated such as a packaging material and the like, under conditions such that the pressure within the vessel is higher than atmospheric pressure and the concentration of the hydrogen peroxide vapor in the treatment vessel is higher than a predetermined level.
Since the hydrogen peroxide vapor supplied into the treatment vessel is easily decomposed and consumed due to contact with the subject to be treated or the wall face inside the vessel, the concentration thereof decreases with the lapse of time. On the other hand, because the sterilization treatment by hydrogen peroxide vapor is performed by means of nascent oxygen generated by the decomposition of hydrogen peroxide, therefore, when the concentration of the hydrogen peroxide vapor decreases to a level less than a certain value, the effective sterilization treatment function cannot be effected. However, it is wasteful from the standpoint of the sterilization treatment to oversupply the hydrogen peroxide vapor into the treatment vessel to maintain the concentration of the vapor higher than a required level. Also, he economic burden is large because, for instance, a treatment device for making the hydrogen peroxide vapor harmless, used when emitting the excess hydrogen peroxide vapor into the air, becomes large sized.
Therefore, in order to perform the sterilization treatment efficiently, it is required to maintain and control the concentration of the hydrogen peroxide vapor in the treatment vessel in a proper concentration range to effect an effective sterilization treatment. In order to control the concentration properly, it is required to detect the concentration of the hydrogen peroxide vapor in the treatment vessel directly and accurately on a real-time basis.
Conventionally, however, a method to detect the concentration of hydrogen peroxide vapor directly and on a real-time basis has not been proposed at all, and the sterilization treatment has thus not been efficiently performed.
Therefore, the inventors of the present invention have tried to detect directly the concentration of the hydrogen peroxide vapor by a controlled potential electrolysis method, test-paper photoelectric photometry, and a method using a detection tube.
Namely, the controlled potential electrolysis method uses a concentration detector (HF sensor) comprising a working electrode and an electrode couple arranged in the region for containing the electrolytic solution, which is separated from the outside world by a partition. And when the hydrogen peroxide vapor permeates the partition and diffuses into the region for containing the electrolytic solution, it is adsorbed to the working electrode comprising an electrochemical catalyst, and causes the oxidation or reduction reaction to generate electric current between the electrodes, thereby detecting the concentration of the hydrogen peroxide vapor by the amount of the generated current.
In such a method, however, not only in the case where the hydrogen peroxide vapor to be detected has extremely low concentration (for example, not higher than 10 ppm), but also in the case of the hydrogen peroxide vapor having concentration as high as the level which permits the sterilization treatment to be sufficiently performed (for example, not lower than 500 ppm), the hydrogen peroxide vapor, the gas to be detected, which has diffused into the electrolytic solution-containing region is adsorbed by the electrolytic solution and remains therein after the concentration has been detected (i.e., after the sterilization treatment has been completed and the hydrogen peroxide vapor within the treatment vessel has been completely removed), and the hydrogen peroxide adsorbed to the working electrode is not eliminated for a long period of time. Therefore, the response to the change in the concentration of the hydrogen peroxide vapor is extremely bad, and the concentration of the hydrogen peroxide vapor cannot be detected accurately on a real-time basis (see FIG. 6).
Furthermore, the test-paper photoelectric photometry uses a concentration detector which incorporates a test paper which is subjected to a special treatment by chemicals so that it is colored by contact with the hydrogen peroxide vapor and detects the concentration of the hydrogen peroxide vapor by the degree of the test paper. In addition to the above-mentioned chemicals, an adequate quantity of water is impregnated into the test paper so as to promote the coloration. In such a method, however, since water is impregnated into the test paper, when the hydrogen peroxide vapor contacts with the test paper, the hydrogen peroxide vapor dissolves in the water contained in the test paper, thereby changing the concentration of the hydrogen peroxide vapor in the vicinity of the concentration detector, with the result that accurate detection of the concentration cannot be performed.
In the sterilization treatment by the hydrogen peroxide vapor, when water adheres to the surface of the object to be treated, the hydrogen peroxide vapor dissolves, as described above, and there is a threat that the sterilization of the object to be treated due to contact with the hydrogen peroxide vapor may be weakened. Therefore, drying treatment may be conducted after the object to be treated is housed in the treatment vessel. When such a drying treatment is performed, however, the test paper which is incorporated in the concentration detector disposed in the treatment vessel is also dried, and the water contained in the test paper is vaporized. Therefore, the detection of the concentration of the hydrogen peroxide vapor using the test paper may not be able to be performed accurately. Moreover, the chemicals impregnated into the test paper may be vaporized by the drying treatment to contaminate the object to be treated. Thus, test-paper photoelectric photometry is inappropriate and cannot be adopted as a detection method for detecting the concentration of the hydrogen peroxide vapor in the sterilization treatment, which needs to be conducted in a low humidity atmosphere.
A method using a detection tube uses a concentration detector, in which a detection agent which changes color by a chemical reaction caused by contact with the hydrogen peroxide vapor is filled in a glass tube, and detects the concentration of the hydrogen peroxide vapor by measuring by the scale of the glass tube the length of the portion of the detection agent whose color has changed. In such a method, however, continuous detection of the concentration cannot be performed, and the concentration of the hydrogen peroxide vapor cannot be detected on a real-time basis.
Thus, neither detection method can detect the concentration of the hydrogen peroxide vapor on a real-time basis, and can be adopted for the treatment of the hydrogen peroxide vapor, such as a sterilization treatment.